1. Field of the Invention
The present invention relates to a transformerless power unit for an electronic apparatus, preferably a horological instrument, including a fluorescent display, with a compensating resistor network which is connected with one pole of the supply voltage, preferably of a series circuit constituted of an ohmic impedance and a capacitor, with a rectifier diode, with a stabilizer for the stabilization of the output direct voltage, and with a charging capacitor which is connected in parallel with the output.
2. Discussion of the Prior Art
Power components of that type can be ascertained, for example, from the disclosure in the handbook "Circuit Examples With Discrete Semi-Conductor Components" (1972 Edition) of the company Intermetall, describing on pages 18 and 19, a stabilizing half-wave rectifier circuit which is operable without a power transformer. Herein, a compensating resistance circuit, which is constituted of a series circuit formed from an ohmic and a capacitive impedance, serves as a compensating resistance for a zener diode. The alternating current voltage present at the zener diode, and which is limited to the zener voltage, is rectified and smoothed through a rectifier diode and a charging capacitor. The zener diode has also a second function in this circuit besides the voltage limiting function (in the blocking direction); it serves in the passing direction for the closing of the alternating current path through the compensating resistor network; in essence, at least the same current flows through this diode as does through the electronic circuit connected thereto. That type of circuit is, accordingly, adapted for simple electronic circuits with a low current requirement, which necessitate only a single direct supply voltage.